The 538 forecasting model is out and it gives Biden a 71 percent chance of an electoral vote win. Relative to other forecasting models like the Economist's and the Princeton Election Consortium, which have Biden's chances at around 9 in 10, that is a fairly conservative assessment. Nate Silver has an explanation post on the model's relative conservatism which is worth reading. This is the key point:
"Joe Biden currently has a robust lead in polls. If the election were held today, he might even win in a landslide, carrying not only traditional swing states such as Florida and Pennsylvania but potentially adding new states such as Georgia and Texas to the Democratic coalition [my note: as you can see in the Nationscape results posted here yesterday]
But the election is not being held today. While the polls have been stable so far this year, it’s still only August. The debates and the conventions have yet to occur. Biden only named his running mate yesterday. And the campaign is being conducted amidst a pandemic the likes of which the United States has not seen in more than 100 years, which is also causing an unprecedented and volatile economy.
Nor has it been that uncommon, historically, for polls to shift fairly radically from mid-August until Election Day. Furthermore, there are some reasons to think the election will tighten, and President Trump is likely to have an advantage in a close election because of the Electoral College.
That, in a nutshell, is why the FiveThirtyEight presidential election forecast, which we launched today, still has Trump with a 29 percent chance of winning the Electoral College, despite his current deficit in the polls. This is considerably higher than some other forecasts, which put Trump’s chances at around 10 percent. Biden’s chances are 71 percent in the FiveThirtyEight forecast, conversely....
The uncertainty in our current 2020 forecast...stems mostly from the fact that there’s still a long way to go until the election. Take what happens if we lie to our model and tell it that the election is going to be held today. It spits out that Biden has a 93 percent chance of winning. In other words, a Trump victory would require a much bigger polling error than what we saw in 2016.
These arguments for baking a lot of uncertainty into the model strikes me as sound. The closer we get to the election, the more the odds for Biden will go up if he maintains his current polling advantage, perhaps reaching the 9 in 10 that other models are already showing. But we ain't there yet.